One step in the manufacture of integrated circuit devices is known as “packaging” and involves mechanical and environmental protection of a semiconductor chip which is at the heart of the integrated circuit as well as electrical interconnection between predetermined locations on the silicon chip and external electrical terminals.
Presently, a number of conventional technologies are employed for packaging semiconductors. Wire bonding, tape automatic bonding (TAB), and flip chip connection are among the packaging techniques used in the industry. Additionally, a so-called “T-contact” connector packaging method is employed by some manufacturers. This “T-contact” method is described in some detail in U.S. Pat. No. 6,040,235 which is hereby incorporated by reference.
Wire bonding employs heat and ultrasonic energy to weld gold bonding wires between bond pads on the chip and contacts on the package.
Tape automatic bonding (TAB) employs a copper foil tape instead of bonding wire. The copper foil tape is configured for each specific die and package combination and includes a pattern of copper traces suited thereto. The individual leads may be connected individually or as a group to the various bond pads on the chip.
Flip chips are integrated circuit dies which have solder bumps formed on top of the bonding pads, thus allowing the die to be “flipped” circuit side down and directly soldered to a substrate. Wire bonds are not required and considerable savings in package footprint may be realized.
Each of the above-described technologies has certain limitations. Both wire bonding and TAB bonding are prone to bad bond formation and subject the die to relatively high temperatures and mechanical pressures. Both wire bond and TAB technologies are problematic from a package size viewpoint, producing integrated circuit devices having a die-to-package area ratio ranging from about 10% to 60%.
The flip-chip does not provide packaging but rather only interconnection. Such interconnection encounters many problems. For example, variations in the uniformity of the solder bumps as well as in thermal expansion mismatching present problems. These difficulties limit the use of available substrates to silicon or materials which have thermal expansion characteristics similar to those of silicon.
The “T-contact” method yields an interconnect structure that is extremely sensitive to process conditions and suffers from reliability problems associated with “T-contact” disassociation. These problems will be described in greater detail hereinbelow.
The difficulties of a known “T-contact” connection can be illustrated with respect to FIGS. 1(a)-1(d). FIG. 1(a) is a cross-section view depicting an edge portion of a semiconductor die 100 that has just been separated from a semiconductor wafer in a singulation process. A silicon substrate 101 having an integrated circuit formed on its surface has been sandwiched between two glass layers 102, 103. Also depicted are the backside solder balls 104 that are used to interconnect the die 100 to other electrical systems. These backside solder balls 104 are connected to front side electrical contact pads 105 by a specialized electrical connection called a “T-contact”. In this view, one such interconnection is shown by the metal layer 107 which makes electrical contact with one of the backside solder balls 104.
FIG. 1(b) is a close-up view depicting the “T-contact” electrical connection shown in the circular view 106 of FIG. 1(a). The backside glass layer 103 affixed to the substrate 101 with a thin epoxy layer 113. On the other side (the front side) of the silicon substrate 101 is a metal bonding pad 111 that is interconnected to the electronic circuitry formed on the silicon substrate 101. Also, on top of the silicon substrate 101 is a first passivation layer 112 that is typically formed of SiO2. Some manufacturers add a second passivation layer 114, formed of benzo-cyclo-butene (BCB), onto the first passivation layer 112. The metal bonding pad 111 is accessible through an opening in the passivation layers 112, 114. Into the opening in the passivation layers 112, 114 is deposited a metal plug 115. Such plugs are commonly formed of Al—Si—Cu compounds (e.g., 94.5% Al, 5.0% Si, and 0.5% Cu). A tab 116 is typically formed over a portion of the passivating layers 112, 114 as shown. The tab 116 portion includes an exposed facet 117 which has an exposed surface.
A top protective layer 102 is attached to the top surface of the substrate 101 using a thin layer of epoxy 118. A metal layer 107 formed on the side of the die 100 forms an electrical contact with the exposed facet 117 thereby forming a conducting pathway to a corresponding solder ball (not shown) on the bottom of the die 100. Commonly, the metal layer 107 is formed of a different material than the plug 115 and tab 116 materials. In one example, the metal layer 107 is constructed of a deposited layer of aluminum/copper (Al/Cu) material. Many other process steps are used to construct such structures. A full description of an example process for constructing such structures is included in the previously referenced U.S. Pat. No. 6,040,235.
Although suitable for some purposes, the aforementioned implementation has some serious drawbacks which will be described with respect to the simplified schematic illustrations of FIGS. 1(c) and 1(d). FIG. 1(c) schematically depicts a simplified cross-section view of an intact “T-contact”. A metal layer 151 is shown in electrical contact with a tab 152 that is electrically connected to a bonding pad (e.g., as in FIG. 1(b)). The connection between the metal layer 151 and the tab 152 is called a “T-contact” 153. Under processing conditions, and also under some operating conditions the “T-contact” 153 can undergo significant stresses. Under some conditions, a separation can occur in the “T-contact” 153 causing electrical connection failure and consequently chip failure. This situation is schematically depicted in FIG. 1(d) which shows a simplified cross-section view of an disconnected “T-contact” 154. The interconnect metal layer 151′ is shown with a break in electrical contact to the contact 152′, thereby breaking the electrical connection to the bonding pad (not shown). The depicted “T-contacts” are very vulnerable to this kind of connection failure. Among the advantages of the disclosed invention is that it substantially reduces the aforementioned type of connection failure.
What is needed is a manufacturable robust electrical connection that does not suffer from “T-contact” failure. Also needed are methodologies for fabricating such structures. The principles of the present invention are directed toward an improved electrical connection and methodologies for its fabrication.